The withdrawal of authorship by the two senators means the proposed Bangsamoro Basic Law (BBL) – which seeks to create an autonomous region initially headed by the Moro Islamic Liberation Front – is no longer guaranteed a majority vote in the Senate.

When the proposed BBL was submitted to the Senate, a total of 13 senators signed up as co-authors. This constitutes a majority vote out of 24 senators, ensuring the passage of the law.

But after clashes where the MILF said it was acting on self defense and killed at least 49 members of the elite Philippine National Police Special Action Force (SAF), Cayetano and Ejercito decided to withdraw their co-authorship.

In a statement, Cayetano said he was "disgusted" with what is happening. He questioned what the purpose of the proposed law was if violence in the South would persist.

"What is the BBL for if they don't have control of the area, and they will say that if 50 policemen died, it's because they did not coordinate?" Cayetano said.

"So I’m withdrawing my co-authorship of the BBL and I seriously doubt if this peace agreement will survive," he added.

Ejercito, meanwhile, condemned "in the highest possible terms" what he said was a massacre of troops.

"I signed as a co-author with the desire of giving the BBL a chance to be the instrument of peace in Mindanao. What happened to the PNP-SAF troopers is not a misencounter but a MASSACRE! I am withdrawing my signature as a co-author of the Bangsamoro Basic Law as a result of this carnage. My heart bleeds for our policemen who were mercilessly killed," Ejercito said.

Other senators, including Senate President Franklin Drilon and Senator Miriam Defensor Santiago, believe that discussions on the proposed law should continue despite the incident. (READ: Maguindanao clash casts doubt on peace process)

Marcos' counterpart at the House of Representatives, Cagayan de Oro Representative Rufus Rodriguez, also gave assurances that the House will continue to push for the passage of the law.

In a separate press briefing, government chief negotiator Miriam Coronel-Ferrer said the Bangsamoro bill proposes long-term solutions to the Mindanao conflict and should not be derailed by a single incident.

The proposed law serves as the legal basis from the final peace agreement between the government and the MILF signed in March 2014 after 17 years of negotiations. It needs to be passed in Congress and in a plebiscite before the envisioned Bangsamoro government can be established. – Rappler.com